sql - 如何使用数据引用的 *_id 字段分隔/格式化 string_agg() 聚合数据？

Question

这个问题是我之前的问题的延续，可以在这里找到。

这个SQLFiddle正在使用我在下面描述的数据库结构和查询。

数据库如下所示：

CREATE TABLE artistnames (
    artistname_id       SERIAL  PRIMARY KEY,
    artistname          TEXT    UNIQUE NOT NULL
);

CREATE TABLE artistalias (
    artistalias_id      SERIAL  PRIMARY KEY,
    artistname_id       SERIAL  REFERENCES artistnames (artistname_id),
    artistalias         TEXT    UNIQUE NOT NULL
);

CREATE TABLE songs (
    song_id             SERIAL  PRIMARY KEY,
    song                TEXT    NOT NULL,
    artistalias_id      SERIAL  REFERENCES artistalias (artistalias_id)
);

• 一位艺术家（表艺术家名称）可以有零个、一个或多个别名
• 一个别名（表 Artistalias）只属于一位艺术家
• 一首歌（桌歌）有一个或多个艺术家（并且指的是他用来表演这首歌的艺术家的别名）

示例：艺术家Francis Veigar还使用别名Francis Fat和Francis Fighter。一首歌曲Song 1以艺人名Francis Veigar发行，另一首歌曲Song 2他使用化名Francis Fat和第三首歌曲Song 3他使用化名Francis Fighter与另一位艺人Peeka Boo一起演唱。

使用查询

SELECT
  string_agg(distinct(artistname), ' & ') AS artist_primary_name,
  string_agg(distinct(a1.artistalias), ' & ') AS performed_song_with_alias, 
  string_agg(a2.artistalias, ' & ') AS other_pseudonymes,
  song
FROM
  artistalias a1
  left JOIN artistalias a2 ON a2.artistname_id = a1.artistname_id
  left JOIN songs s ON s.artistalias_id = a1.artistalias_id
  left JOIN artistnames ON artistnames.artistname_id = a1.artistname_id
GROUP BY song;

显示other_pseudonymes列

+----------------------------+-----------------------------+--------------------------------------------------------------------+--------+
| artist_primary_name        | performed_song_with_alias   | other_pseudonymes                                                  | song   |
+----------------------------+-----------------------------+--------------------------------------------------------------------+--------+
| Francis Veigar             | Francis Veigar              | Francis Veigar & Francis Fat & Francis Fighter                     | Song 1 |
+----------------------------+-----------------------------+--------------------------------------------------------------------+--------+
| Francis Veigar             | Francis Fat                 | Francis Veigar & Francis Fat & Francis Fighter                     | Song 2 |
+----------------------------+-----------------------------+--------------------------------------------------------------------+--------+
| Francis Veigar & Peeka Boo | Francis Fighter & Peeka Boo | Francis Veigar & Francis Fat & Francis Fighter & Peeka Boo & Peeka | Song 3 |
+----------------------------+-----------------------------+--------------------------------------------------------------------+--------+
| Peeka Boo                  | Peeka                       | Peeka Boo & Peeka                                                  | Song 4 |
+----------------------------+-----------------------------+--------------------------------------------------------------------+--------+

我希望它看起来像

+----------------------------+-----------------------------+--------------------------------------------------------------------+--------+
| artist_primary_name        | performed_song_with_alias   | other_pseudonymes                                                  | song   |
+----------------------------+-----------------------------+--------------------------------------------------------------------+--------+
| Francis Veigar             | Francis Veigar              | Francis Veigar & Francis Fat & Francis Fighter                     | Song 1 |
+----------------------------+-----------------------------+--------------------------------------------------------------------+--------+
| Francis Veigar             | Francis Fat                 | Francis Veigar & Francis Fat & Francis Fighter                     | Song 2 |
+----------------------------+-----------------------------+--------------------------------------------------------------------+--------+
| Francis Veigar & Peeka Boo | Francis Fighter & Peeka Boo | Francis Veigar & Francis Fat & Francis Fighter / Peeka Boo & Peeka | Song 3 |
+----------------------------+-----------------------------+--------------------------------------------------------------------+--------+
| Peeka Boo                  | Peeka                       | Peeka Boo                                                          | Song 4 |
+----------------------------+-----------------------------+--------------------------------------------------------------------+--------+

用“/”分隔两位不同艺术家使用的假名/别名。在查询中必须改变什么来实现这一点？

Answer 1

使用子查询，然后SELECT使用聚合元素并string_agg再次使用：

SELECT
  string_agg(distinct(artistname), ' & ') AS artist_primary_name,
  string_agg(distinct(a1.artistalias), ' & ') AS performed_song_with_alias, 
  string_agg(distinct(col),' / ') AS other_pseudonymes,
  song
FROM
  artistalias a1
  left JOIN artistalias a2 ON a2.artistname_id = a1.artistname_id
  left JOIN songs s ON s.artistalias_id = a1.artistalias_id
  left JOIN artistnames ON artistnames.artistname_id = a1.artistname_id
  left join 
(SELECT 
    string_agg(a2.artistalias, ' & ') as col,
    artistname_id 
 FROM artistalias a2
 GROUP BY artistname_id)
AS aggregated_aliases ON aggregated_aliases.artistname_id = artistnames.artistname_id
GROUP BY song;